how was the society of the Roman republic organized? how did it balance the dangers of internal division and external invasion?

how is this answer:
The society of the Roman Republic was divided into two groups: the plebians and the patricians. The patrician group consisted of aristocratic families with lots of land, descended from Rome's original senators. They controlled the centuriate assembly and many other parts of Roman life, along with being the only people able to be consuls, magistrates and senators. The plebians,on the other hand, were a much larger group consisting of landholders, artisans, merchants and small farmers. They were citizens, but did not have the same rights as patricians, as they could not be elected to government offices and could not marry patricians. However to balance the danger of internal division between these classes, the council of the plebs was created to gain many rights for the plebian, making them almost equal with the patricians, though it was not a democracy.